A need for high-quality, high-speed computer printers and other output printers with changeable formats has been evidenced in recent years. Developments have proceeded with respect to ink jet technology in an effort to answer this need. Many of the developments in the field of ink jet have related to pressurized ink jet systems wherein a stream or streams of ink are ejected from one or more orifices in the form of filaments and perturbated so that each filament breaks into a stream of uniformly sized droplets.
Examples of such systems include magnetic ink jet wherein droplets of magnetic ink are selectively deflected to a recording medium or to a gutter. Another example comprises electrostatic deflected ink jet such as taught by Sweet U.S. Pat. No. 3,596,275, wherein a single stream of droplets are selectively charged and passed through a uniform deflection field to impact various locations on a recording medium in accordance with the charge of each droplet. Thus, by applying suitable charging signals to the droplets, readable printed characters may be formed on the recording surface. Still another example comprises electrostatic binary ink jet such as taught by Sweet et al, U.S. Pat. No. 3,373,437. This type of system generates a plurality of jets in one or more rows, selectively charging droplets with a single charge level for deflection by a constant field to an ink drop catcher. The uncharged drops continue undeflected along the original jet path to impact the recording surface and form readable printed characters.
It appears that good print quality for printed characters requires that the lines forming character comprise more than a single row of spots resulting from the impact of ink jet droplets. Hence, the droplets required to form characters must be of an extremely small size. If the droplets are small, the spots formed therefrom may be sufficiently small and closely spaced so as to be relatively indiscernible as individual drops, but rather discernible only as part of the resultant printed symbol.
The most important factor in producing small droplets is the diameter of the orifice through which the ink is ejected. For example, to achieve a spot diameter of less than seven mils in diameter requires orifices no larger than two mils in diameter. Orifices may even reach less than one mil in diameter.
Orifices of such size are easily clogged by small particles of foreign material even though advanced filtering techniques are used.
An object of the present invention is to provide an ink jet head structure which allows cleaning of certain clogs and removal of the foreign material.